1. Field of the Invention
This invention relates to molded case circuit breakers, and more particularly to a mechanical trip interlock assembly for automatically tripping the circuit breaker when the circuit breaker is removed or lifted away from its panel mounting when a manual override for tripping the circuit breaker has not been operated.
2. Description of the Prior Art
Circuit breakers are generally well-known in the art. Examples of molded case circuit breakers are disclosed in U.S. Pat. Nos. 4,489,295; 4,638,277; 4,642,430; 4,656,444; 4,679,018; and 4,963,846. Circuit breakers are used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload and relatively high level short circuit conditions.
Certain types of molded case circuit breakers have mounted within their housing a modular trip unit which includes a trigger or latching assembly, which under normal conditions latches a cradle operatively coupled to one or more main contacts. Actuation of the modular trip unit unlatches the cradle which causes the contacts to separate, which, in effect, interrupts the flow of current through the circuit breaker from the line side to the load side.
Molded case circuit breakers include at least one pair of separable contacts which generally may be operated manually by way of a handle disposed on the outside of the case or automatically in response to an overcurrent condition. When the circuit breaker is on, the movable contact assembly being in contact with the stationary contact assembly, provides a flow of current between the line and load terminals. When the circuit breaker trips or is switched off, the movable contact assembly is moved away from the stationary contact assembly, thus, interrupting the flow of current from the line terminals to the load terminals.
An electronic trip unit may be provided for interrupting the current flow, and is generally operated automatically or manually by way of a pushbutton. When the pushbutton is pressed, a plunger associated with the pushbutton causes a trip bar to rotate to trip the circuit breaker.
In an automatic mode of operation for the electronic trip unit, the contact assemblies for all poles are tripped together by the electronic trip unit which operates a mechanical operating mechanism. The electronic trip unit is provided with current sensors which respond to an overcurrent condition. When an overcurrent condition is sensed, the current transformers provide a signal to the electronic circuitry within the electronic trip unit to actuate the operating mechanism to cause the main contacts of the poles to be separated.
A circuit breaker also includes a cradle having latch and reset surfaces for latching and resetting the operating mechanism. A molded case circuit breaker further includes a molded base and a coextensive cover. A centrally located aperture is provided in the cover for receiving an operating handle to allow the circuit breaker to be operated manually. The handle is comprised of an arcuate shaped base portion with a radially extending hand portion.
A common type of circuit breaker has a handle which moves linearly between an on and an off position. The handle is connected to the movable contacts of the circuit breaker through a spring powered, over center toggle device which trips the contacts open and moves the handle to an intermediate position in response to certain overcurrent conditions.
Sometimes it is necessary to remove a circuit breaker from its panel mounting after it has been placed in service. For example, the circuit breaker may need to be removed for servicing or maintenance. Additionally, the circuit breaker may have to be removed and replaced with another circuit breaker with a different current rating due to a change in the load requirements.
Circuit breakers with plug in type rear terminations may be removed from the circuit breaker panel by unfastening the circuit breaker and pulling it outwardly from the panel. Such action will disconnect the circuit breaker load side and line side terminations from the corresponding receptacles on the circuit breaker panel. If the circuit breaker is on and is supplying electrical power to a load, electrical current will be flowing through the circuit breaker line side and load side terminations and corresponding receptacles on the circuit breaker panel. Should the circuit breaker be removed from its panel mounting while electrical current is flowing therethrough the electrical circuit would be broken between the terminations on the circuit breaker and the corresponding receptacles on the panel causing an arc to be drawn therebetween.
In some of the known circuit breakers it is incumbent on the operator to manually trip the circuit breaker before removing it from the panel. This is done either by a trip button, or if there is no trip button, the operator manually turns the handle to the "off" positioning.
In circuit breakers such as disclosed in Grunert, et al., U.S. Pat. No. 4,963,846, assigned to Westinghouse Electric Corporation, there is a device for automatically tripping the circuit breaker prior to its being removed from the panel. This device is referred to as "a trip interlock assembly," which trips the circuit breaker any time the circuit breaker is removed from its panel mounting. This trip interlock assembly is adapted to be disposed adjacent a load side terminal and cooperates with the circuit tripping means. In one embodiment, the trip interlock assembly includes a housing and a spring-loaded actuation arm disposed generally perpendicular to the circuit breaker panel surface. The actuation arm is formed with a cam surface which cooperates with a trip pin, reciprocally mounted with respect to the circuit breaker tripping means. The trip pin acts as a cam follower and rides along the cam surface formed in the actuation arm. When the actuation arm is in an inward position indicating that the circuit breaker is mounted against a panel, the trip pin will not actuate the tripping means. However, when the circuit breaker is removed from the panel, the actuation arm, under the influence of a biasing spring moves outwardly, which, in turn, causes the cam surface on the actuation arm to move outwardly. This action causes the trip pin to move inwardly with respect to the trip unit and actuate the tripping means, which, in turn, trips the circuit breaker.
In an alternative embodiment of the invention of U.S. Pat. No. 4,963,846, the trip interlock assembly includes a bell crank interlock with a reciprocally mounted plunger which actuates an armature in the tripping means directly instead of by way of the trip pin any time the circuit breaker is removed from its panel housing.
A disadvantage of the trip interlock assembly of the prior art such as that of this U.S. Pat. No. 4,963,846 is the fact that its design requires it to be disposed adjacent to either a load or a line side terminal for its mounting and interconnection to the circuit breaker.
There remains a need for a modular tripping unit which has a trip interlock assembly which is built inside a housing of a modular trip unit.